Proton Environment Optimization Enhanced Asymmetric C 1 –C 2 Intermediate Coupling for CO 2 Reduction to n‐Propanol

ABSTRACT The electrochemical conversion of CO 2 into value‐added n‐propanol (n‐PrOH) product is pivotal for establishing a sustainable carbon cycle. However, the process is severely hindered by the kinetically sluggish and uncontrolled asymmetric C 1 –C 2 coupling step. Here, we develop a proton modulation strategy to optimize the CO 2 ‐to‐C 3 pathway. Structural engineering of the gas diffusion electrode modulates the H 2 O network environment at the triphasic interface, establishing a gradient H + concentration environment that avoids the direct hydrogenation of *C 2 intermediates. The Faradaic efficiency (FE) for n‐PrOH reaches 21% at a partial current density of 167.5 mA cm −2 in a flow cell. In the membrane electrode assembly, the FE n‐PrOH remains 19% at a partial current density of 132.9 mA cm −2 . Mechanistic investigations identify *OCH 2 CH 3 as the pivotal intermediate in n‐PrOH formation. The simultaneous reduction of the formation energy barriers for both the C 1 –C 1 and C 1 –C 2 coupling rate‐determining steps drives C 3 product formation. This work highlights the significant role of proton environment engineering as a crucial parameter in the selection of the C 3 product pathway.